1. Field of the Invention
The present invention relates to spraying such as painting wherein a substance to be sprayed is dispersively supplied toward an article which represents the object to be sprayed with that substance.
2. Description of the Related Art
It is known in spraying techniques that the distance between a spray apparatus and an object to be sprayed (said distance being hereinafter referred to as "spray distance") is an important factor to be taken account of if spraying is to be undertaken effectively. In painting, for example, a uniform spray pattern and a preferable coating thickness can be obtained when the spray distance is coincident with a predetermined value which is determined by the spraying conditions of each individual spray apparatus. The fact that the spray distance has a given preferable value for each individual spray apparatus applies not only to cases where the substance to be sprayed is a liquid but also to cases where the spray substance is a finely divided solid as in the case of power painting. In addition, the above-described fact also applies to cases where articles are subjected to spraying when being treated with various kinds of chemical agents, water, adhesives or the like.
There are known methods of maintaining the spray distance at an optimal value at all times. In one type of such conventional methods, the distance from a spray apparatus to an article is detected, and the spray apparatus is moved on the basis of the detected distance so that the spray distance is maintained at a constant value (e.g., the one mentioned in the specification of Japanese Patent Public Disclosure No. 17864/1983 published on Feb. 2, 1983). In another type of such prior art methods, the configuration of an article is stored in a memory in advance, and a spray apparatus is moved on the basis of the stored data so that the spray distance is maintained at a constant value (e.g., the one mentioned in the specification of Japanese Patent Public Disclosure No. 88064/1983 publicly disclosed on May 26, 1983). These prior art spraying methods, however, require a mechanism for automatically moving the spray apparatus in the direction in which the distance to the article is varied, resulting in an increase in the size of the apparatus as a whole, and it is impossible to apply these methods to portable spraying apparatuses which are so designed as to be handheld in used.